[clang] [Clang] Eagerly instantiate used constexpr function upon definition. (PR #73463)

[Sam McCall via cfe-commits]

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@@ -4836,6 +4837,16 @@ ASTFileSignature ASTWriter::WriteASTCore(Sema &SemaRef, StringRef isysroot,
   assert(SemaRef.PendingLocalImplicitInstantiations.empty() &&
          "There are local ones at end of translation unit!");
 
+  // Build a record containing all pending instantiations of constexpr
+  // entities.
+  RecordData PendingInstantiationsOfConstexprEntities;
+  for (const auto &I : SemaRef.PendingInstantiationsOfConstexprEntities) {
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sam-mccall wrote:

In case this will be relanded in some form:

This loop uses arbitrary hashtable order, leading to nondeterministic PCM output.

https://github.com/llvm/llvm-project/pull/73463